There should be exactly one hose that passes from the engine compartment to the interior. It runs in near the brake booster. Disconnect the lines there, opening the body area to fresh air and then cap off the engine compartment side.
Now, get yourself a little vacuum pump (about 30$) and use it to charge the interior side of the system. If the door locks suddenly work, I'd be surprised, and that would point under the hood for your problem.
If the door locks still don't work, you can ignore the under the hood stuff and ask for the interior vacuum routing schematic.
Send me an email, if I can find it, I'll reply with it as an attachment.